The invention relates to devices for administering, injecting, delivering or dispensing substances, and to methods of making and using such devices. More particularly, it relates to a device for administering an injectable product wherein the device may be an automatic injector.
Injection devices of the type to which the invention relates are known from DE 198 22 031 B and U.S. Pat. No. 4,031,893. Both documents describe automatic injectors. In the case of the automatic injector disclosed in DE 198 22 031 A1, a mechanical sequence controller ensures that once the device has been triggered, the injection cannula is inserted through the skin to the desired depth in a first phase and the product to be injected is not dispensed and administered until a subsequent second phase. The injection device disclosed in U.S. Pat. No. 4,031,893 does not have such a sequence controller. Instead, a drive mechanism applies pressure to push a plunger disposed in a container filled with the product, and both the container and hence also the injection cannula and the plunger in the container are pushed in a forward direction due to static friction. The insertion and dispensing procedures do not, therefore, take place exactly sequentially and instead also take place simultaneously to a certain extent.
The plunger of the respective devices is driven forwards by means of a plunger rod and a spring acting on the plunger rod in the forward-drive (or injection or delivery) direction of the plunger. In the case of the devices disclosed in DE 198 22 031 A1, the spring is accommodated in a drive cup and pushes the cup against a proximal end of the plunger rod. In the simplified design disclosed in U.S. Pat. No. 4,031,893, the spring directly surrounds the plunger rod and pushes in the forward direction against a shoulder of the plunger rod which projects radially outwards. The plunger rod is either fixedly connected to the plunger directly or is connected to an intermediate piece fixedly connected to the plunger, which serves as an adapter for adapting to different filling levels of the container.
In order to improve handling, it is desirable to make devices for administering injectable products as compact as possible, and, in particular, with as short as possible a length as measured in the forward-drive direction of the plunger. This is particularly desirable in the case of automatic injectors because automatic injectors are generally longer than conventional injection devices, including simple syringes, simply because the injection cannula has to be moved an extra distance in the forward-drive direction relative to a housing to account for the insertion depth desired for the injection.